Vitamin E by alsalhi

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									                           Vitamin E
Vitamin E: What is it?
Vitamin E is a fat-soluble vitamin that exists in eight different forms.
Each form has its own biological activity, which is the measure of
potency or functional use in the body . Alpha-tocopherol (α-tocopherol) is
the name of the most active form of vitamin E in humans. It is also a
powerful biological antioxidant. Vitamin E in supplements is usually sold
as alpha-tocopheryl acetate, a form that protects its ability to function as
an antioxidant. The synthetic form is labeled "D, L" while the natural
form is labeled "D". The synthetic form is only half as active as the
natural form.

Antioxidants such as vitamin E act to protect your cells against the effects
of free radicals, which are potentially damaging by-products of energy
metabolism. Free radicals can damage cells and may contribute to the
development of cardiovascular disease and cancer. Studies are underway
to determine whether vitamin E, through its ability to limit production of
free radicals, might help prevent or delay the development of those
chronic diseases. Vitamin E has also been shown to play a role in immune
function, in DNA repair, and other metabolic processes.

What foods provide vitamin E?
Vegetable oils, nuts, green leafy vegetables, and fortified cereals are
common food sources of vitamin E in the United States (U.S.). Table 1,
Selected Food Sources of Vitamin E, suggests many food sources of
vitamin E . Food values are listed in alpha-tocopherol equivalents (ATE)
to account for the variation in biological activity of the different forms of
vitamin E.


What is the recommended intake for vitamin E?
Recommendations for vitamin E are provided in the Dietary Reference
Intakes developed by the Institute of Medicine. Dietary Reference Intakes
(DRIs) is the general term for a set of reference values used for planning
and assessing nutrient intake for healthy people. Three important types of
reference values included in the DRIs are Recommended Dietary
Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake


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Levels (UL). The RDA recommends the average daily dietary intake level
that is sufficient to meet the nutrient requirements of nearly all (97-98%)
healthy individuals in each age and gender group.

An AI is set when there is insufficient scientific data available to establish
a RDA. AIs meet or exceed the amount needed to maintain a nutritional
state of adequacy in nearly all members of a specific age and gender
group. The UL, on the other hand, is the maximum daily intake unlikely
to result in adverse health effects.

In Table1, RDAs for vitamin E are listed as Alpha-Tocopherol
Equivalents (ATE) to account for the different biological activities of the
various forms of vitamin E. Table 1 also lists RDAs for vitamin E in
International Units (IU) because food and some supplement labels list
vitamin E content in International Units (1 mg ATE vitamin E = 1.5 IU).

Table 1: Recommended Dietary Allowances for Vitamin E for
Children and Adults
  Age Children        Men      Women Pregnancy Lactation
(years) (mg/day) (mg/day) (mg/day) (mg/day) (mg/day)
           6 mg
1-3
          (=9 IU)
           7 mg
4-8
        (=10.5 IU)
                     11 mg      11 mg      15 mg      19 mg
9-13
                   (=16.5 IU) (=16.5 IU) (=22.5 IU) (=28.5 IU)
                     15 mg      15 mg      15 mg      19 mg
14 +
                   (=22.5 IU) (=22.5 IU) (=22.5 IU) (=28.5 IU)


There is insufficient scientific data on vitamin E to establish an RDA for
infants. An Adequate Intake (AI) has been established that is based on the
amount of vitamin E consumed by healthy infants who are fed breast
milk. Table 2 lists the adequate intakes for vitamin E for infants in mg
ATE and IUs (1 mg ATE vitamin E = 1.5 IU).




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Table 2: Adequate Intake for Vitamin E for Infants
   Age Males and Females
(months)     (mg/day)
                4 mg
0 to 6
               (=6 IU)
                5 mg
7 to 12
              (=7.5 IU)


Results of two national surveys, the National Health and Nutrition
Examination Survey (NHANES III 1988-94) and the Continuing Survey
of Food Intakes by Individuals (1994-96 CSFII) indicated that diets of
most Americans do not provide the recommended intake for vitamin E.
However, an Institute of Medicine (IOM) report on vitamin E published
in 2000 states that intake estimates of vitamin E may be low because
energy and fat intake are often underreported in national surveys and
because the kind and amount of fat added during cooking is often not
known. The IOM states that most North American adults get enough
vitamin E from their normal diets to meet current recommendations.
However, they do caution that low fat diets can result in a significant
decrease in vitamin E intake. "Low-fat diets can substantially decrease
vitamin E intakes if food choices are not carefully made to enhance α-
tocopherol intakes".

Who is at risk for vitamin E deficiency?

Vitamin E deficiency is rare in humans. There are three specific situations
when a vitamin E deficiency is likely to occur.

   1. persons who cannot absorb dietary fat due to an inability to secrete
      bile or with rare disorders of fat metabolism are at risk of vitamin E
      deficiency];
   2. individuals with rare genetic abnormalities in the alpha-tocopherol
      transfer protein are at risk of vitamin E deficiency; and
   3. premature, very low birth weight infants (birth weights less than
      1500 grams, or 3 pounds, 4 ounces) are at risk of vitamin E
      deficiency.

Blood levels of vitamin E may also be decreased with zinc deficiency.
Vitamin E deficiency is usually characterized by neurological problems
associated with nerve degeneration in hands and feet. These symptoms
are also associated with other medical conditions. A physician can

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determine if they are the result of a vitamin E deficiency or are from
another cause.

Who may need extra vitamin E to prevent a deficiency?

Individuals who cannot absorb fat require a vitamin E supplement
because some dietary fat is needed for the absorption of vitamin E from
the gastrointestinal tract. Intestinal disorders that often result in
malabsorption of vitamin E and may require vitamin E supplementation
include:

      Crohn's Disease is an inflammatory bowel disease that affects the
       small intestines. People with Crohn's disease often experience
       diarrhea and nutrient malabsorption.
      Cystic Fibrosis is an inherited disease that effects the lungs,
       gastrointestinal tract, pancreas, and liver. Cystic fibrosis can
       interfere with normal digestion and absorption of nutrients,
       especially of fat soluble vitamins including vitamin E.

People who cannot absorb fat often pass greasy stools or have chronic
diarrhea. People with an inability to secrete bile, a substance that helps fat
digestion, may need a special water-soluble form of vitamin E.

Abetalipoproteinemia is a rare inherited disorder of fat metabolism that
results in poor absorption of dietary fat and vitamin E. The vitamin E
deficiency associated with this disease causes problems such as poor
transmission of nerve impulses, muscle weakness, and degeneration of
the retina that can cause blindness. Individuals with abetalipoproteinemia
may be prescribed special vitamin E supplements by a physician to treat
this disorder.

Ataxia and vitamin E deficiency (AVED) is also a rare inherited disorder.
It is caused by a genetic defect in a liver protein that is responsible for
maintaining normal alpha-tocopherol concentrations in the blood. These
individuals have such severe vitamin E deficiency that without
supplements they are unable to walk (ataxia).

Very low birth weight infants may be deficient in vitamin E. Necrotizing
enterocolitits, a condition sometimes seen in very low birth weight infants
that is characterized by inflammation of the lining of the intestines, may
lead to a vitamin E deficiency. These infants are usually under the care of
a neonatologist, a pediatrician specializing in the care of newborns who
evaluates and treats the exact nutritional needs of premature infants.


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What are some current issues and controversies about vitamin E?

Vitamin E and heart disease
Preliminary research has led to a widely held belief that vitamin E may
help prevent or delay coronary heart disease. Researchers have reported
that oxidative changes to LDL-cholesterol (sometimes called "bad"
cholesterol) promote blockages (atherosclerosis) in coronary arteries that
may lead to heart attacks. Vitamin E may help prevent or delay coronary
heart disease by limiting the oxidation of LDL-cholesterol. Vitamin E
also may help prevent the formation of blood clots, which could lead to a
heart attack. Observational studies have associated lower rates of heart
disease with higher vitamin E intake. A study of approximately 90,000
nurses suggested that the incidence of heart disease was 30% to 40%
lower among nurses with the highest intake of vitamin E from diet and
supplements. Researchers found that the apparent benefit was mainly
associated with intake of vitamin E from dietary supplements. High
vitamin E intake from food was not associated with significant cardiac
risk reduction. A 1994 review of 5,133 Finnish men and women aged 30-
69 years also suggested that increased dietary intake of vitamin E was
associated with decreased mortality (death) from heart disease.

Even though these observations are promising, randomized clinical trials
raise questions about the efficacy of vitamin E supplements in the
prevention of heart disease. The Heart Outcomes Prevention Evaluation
(HOPE) Study followed almost 10,000 patients for 4.5 years who were at
high risk for heart attack or stroke. In this intervention study the subjects
who received 265 mg (400 IU) of vitamin E daily did not experience
significantly fewer cardiovascular events or hospitalizations for heart
failure or chest pain when compared to those who received a placebo
(sugar pill). The researchers suggested that it is unlikely that the vitamin
E supplement provided any protection against cardiovascular disease in
the HOPE study. This study is continuing, with the goal of determining
whether a longer duration of intervention with vitamin E supplements
will provide any protection against cardiovascular disease.

In a study sponsored by the National Heart, Lung, and Blood Institute
(NHLBI) of the National Institutes of Health, postmenopausal women
with heart disease who took supplements providing 400 IU vitamin E and
500 mg vitamin C twice a day, either alone or in combination with
hormones, did not have fewer heart attacks or deaths. There was also no
change in progression of their coronary disease. This study, The Women's
Angiographic Vitamin and Estrogen (WAVE) trial, studied 423
postmenopausal women at seven clinical centers in the U.S. and Canada.


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In postmenopausal women with coronary disease enrolled in this trial,
neither hormone replacement therapy nor antioxidant vitamin
supplements provided cardiovascular benefit.

Results of the Women's Health Study, the Women's Antioxidant and
Cardiovascular Study and the SuVIMAX study, all of which are
investigating the effects of vitamin supplements on the progression of
coronary heart disease, are due in 2005 and will provide additional
information on the association between vitamin E supplements and
cardiovascular disease.


Vitamin E and cancer
Antioxidants such as vitamin E are believed to help protect cell
membranes against the damaging effects of free radicals, which may
contribute to the development of chronic diseases such as cancer. Vitamin
E also may block the formation of nitrosamines, which are carcinogens
formed in the stomach from nitrites consumed in the diet. It also may
protect against the development of cancers by enhancing immune
function. Unfortunately, human trials and surveys that have tried to
associate vitamin E intake with incidence of cancer have been generally
inconclusive.

Some evidence associates higher intake of vitamin E with a decreased
incidence of prostate cancer and breast cancer. However, an examination
of the effect of dietary factors, including vitamin E, on incidence of
postmenopausal breast cancer in over 18,000 women from New York
State did not associate a greater vitamin E intake with a reduced risk of
developing breast cancer.

A study of women in Iowa provides evidence that an increased dietary
intake of vitamin E may decrease the risk of colon cancer, especially in
women under 65 years of age. On the other hand, a study of 87,998
females from the Nurses' Health Study and 47,344 males from the Health
Professionals Follow-up Study failed to support the theory that an
increased dietary intake of vitamin E may decrease the risk of colon
cancer.

The American Cancer society recently released the results of a long-term
study that evaluated the effect of regular use of vitamin C and vitamin E
supplements on bladder cancer mortality in almost 1,000,000 adults in the
U.S. The study, conducted between the years 1982 to 1998, found that
subjects who regularly consumed a vitamin E supplement for longer than


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10 years had a reduced risk of death from bladder cancer. No benefit was
seen from vitamin C supplements.

At this time researchers cannot confidently recommend vitamin E
supplements for the prevention of cancer because the evidence on this
issue is inconsistent and limited.


Vitamin E and cataracts
Cataracts are abnormal growths in the lens of the eye. These growths
cloud vision. They also increase the risk of disability and blindness in
aging adults. Antioxidants are being studied to determine whether they
can help prevent or delay cataract growth. Observational studies have
found that lens clarity, which is used to diagnose cataracts, was better in
regular users of vitamin E supplements and in persons with higher blood
levels of vitamin E. A study of middle-aged male smokers, however, did
not demonstrate any effect from vitamin E supplements on the incidence
of cataract formation. The effects of smoking, a major risk factor for
developing cataracts, may have overridden any potential benefit from the
vitamin E, but the conflicting results also indicate a need for further
studies before researchers can confidently recommend extra vitamin E for
the prevention of cataracts.

What is the health risk of too much vitamin E?

Most studies of the safety of vitamin E supplementation have lasted for
several months or less, so there is little evidence for the long-term safety
of vitamin E supplementation.

ODS is working on updating this section of the vitamin E fact sheet to
include the results of meta-analyses and clinical trials that have been
published recently. A new version will be posted shortly.

The Food and Nutrition Board of the Institute of Medicine has set an
upper tolerable intake level (UL) for vitamin E at 1,000 mg (1,500 IU) for
any form of supplementary alpha-tocopherol per day. Based for the most
part on the result of animal studies, the Board decided that because
vitamin E can act as an anticoagulant and may increase the risk of
bleeding problems this UL is the highest dose unlikely to result in
bleeding problems.




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Table 3 lists the Tolerable Upper Intake Levels (UL) of vitamin E in mg
ATE and IUs for children and adults (1 mg ATE vitamin E = 1.5 IU). A
UL for vitamin E for infants up to 12 months of age has not been
established.

Table 3: Tolerable Upper Intake Levels (UL) of vitamin E for
Children and Adults
               Males      Females Pregnancy Lactation
Age (years)
             (mg/day) (mg/day) (mg/day) (mg/day)
                200         200         N/A         N/A
1-3
             (=300 IU) (=300 IU)
                300         300         N/A         N/A
4-8
             (=450 IU) (=450 IU)
                600         600         N/A         N/A
9-13
             (=900 IU) (=900 IU)
                800         800         800         800
14-18
            (=1,200 IU) (=1,200 IU) (=1,200 IU) (=1,200 IU)
               1,000       1,000       1,000       1,000
19-70
            (=1,500 IU) (=1,500 IU) (=1,500 IU) (=1,500 IU)
               1,000       1,000        N/A         N/A
> 70
            (=1,500 IU) (=1,500 IU) (=1,500 IU) (=1,500 IU)


Selecting a Healthful Diet

As the 2000 Dietary Guidelines for Americans state, "Different foods
contain different nutrients and other healthful substances. No single food
can supply all the nutrients in the amounts you need". Many people are
concerned about their fat intake today. Your overall diet should be
moderate in fat, but it is important to include some healthful sources of
fat, including those oils and nuts that provide vitamin E. Including these
foods in your diet will help you meet your daily need for vitamin E.
Meats, grain products, dairy products, and most fruits and vegetables are
generally not good sources of vitamin E.




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